1. Field of the Invention
The present invention relates to a polycarbonate resin composition comprising a polycarbonate resin with a specific structure and a method of producing the same. Specifically, the present invention relates to a polycarbonate resin composition comprising a polycarbonate resin with a specific structure so that it is appropriate as an optical material having high transparency, high resistance to heat, high refractive index and low birefringence, and a method of producing the same.
2. Description of the Related Art
A polycarbonate resin which is obtained by reacting 2,2-bis(4-hydroxyphenyl)propane (common name: bisphenol A) with phosgene or carbonic acid diester has an excellent resistance to heat and excellent transparency. In addition, as having an excellent mechanical property such as impact resistance, etc., it is widely used not only as a structural material but also as an optical material like a plastic optical product including various lenses, prisms, optical disc substrates, optical fibers and the like and an optical film.
However, since the conventional aromatic polycarbonate resins are a material having high optical elasticity and low fluidity, it has a problem that birefringence is high due to molecular orientation during molding and residual stress. Thus, when an optical material consisting of conventional aromatic polycarbonate resin is molded, a method of using a resin with relatively low molecular weight to improve fluidity and molding at high temperature to reduce birefringence of a product has been used. However, with the conventional aromatic polycarbonate resins, birefringence can be only limitedly reduced even when such method is employed. Thus, in accordance with enlarged use of an optical material in recent days, development of a material which has even lower optical elasticity coefficient and high fluidity has been really waited for in several optical material fields. In this connection, development of a resin having even smaller birefringence has been carried out.
Meanwhile, if an optical material has high refractive index, even smaller curvature of the surface of a lens element can be achieved. As a result, aberration amount occurring on the surface can be reduced and small scale and lightweight production of a lens system can be achieved based on reduction in the number of lenses, reduction in the eccentric sensitivity of a lens and reduction in the thickness of a lens. In addition, an eyeglass lens can provide excellent appearance as thinning of a lens with the same power of eyeglasses can be achieved.
Thus, development of an optical resin having high refractive index and low birefringence has been carried out, and as such optical resin having high refractive index and low birefringence, a wholly aromatic polycarbonate resin copolymer using bisphenols with a fluorene structure has been studied (see, Patent Document Nos. 1 and 2 below).
Further, a homopolycarbonate resin of ether diols having a phenol skeleton and a fluorene structure, or a copolymer of such resins and bisphenols is disclosed (see, Patent Document Nos. 3 and 4 below).
Still further, a copolymer of bisphenols having a fluorene structure and tricyclodecane[5.2.1.02,6]dimethanol is also suggested (see, Patent Document No. 5 below).    [Patent Document No. 1] Japanese Patent Application Laid-Open (JP-A) No. 6-25398    [Patent Document No. 2] JP-A No. 7-109342    [Patent Document No. 3] JP-A No. 10-101787    [Patent Document No. 4] JP-A No. 10-101786    [Patent Document No. 5] JP-A No. 2000-169573